1. Field of the Invention
The present invention relates to a multifocal contact lens and methods of making the same and, more specifically, it relates to such a multifocal lens which facilitates simultaneous near and distant vision without having disruptive junctions between areas designed to facilitate such vision.
2. Description of the Prior Art
It has been known for individuals who require corrective vision for either distance viewing or near viewing, or both, to provide corrective eyeglasses which have, within the lens for each eye, a first segment adapted for distance vision and a second segment to be viewed separately for near vision.
It has also been known to provide trifocals which have three separate corrective lenses incorporated into a single lens. Such eyeglasses typically have very prominent divider lines between adjacent lens sections, which can be disruptive to one using the same.
It has also been known to attempt to provide eyeglasses with a transition zone between adjacent lens sections in a single lens to minimize the sometimes visually annoying prominent line of demarcation. Such transition zones typically provide for a blurred region between the two lenses as distinguished from a specific linear border.
It is also known that the sharp dividing line or the blending of the dividing line creates a small, optically useless, area of the lens. A measure of success occurs in eyeglasses because the lens is held stationary by the frame and the eyes can turn to select an area of the lens where these optical distractions will not enter the pupil. This is also the case with the translating bifocal or trifocal contact lens wearer whose lens must be fit loose enough for the eye to slide with respect to the lens, thereby allowing the pupil to line up with the appropriate segment of the lens.
It is also known that these segment boundaries are an optical problem with a simultaneous vision contact lens that has to center on the eye. All of these optical distractions, by position of the lens, must enter the pupil at the same time.
It is also known that the optical industry has created a progressive, variable focus, aspheric, multifocal spectacle lens. The distance vision part of the lens is disposed from the center of the pupil upward and the lens power can be confirmed with the lensometer. From the center of the pupil, downward, there is an aspheric curve that gradually increases in power to its full reading power near the bottom of the lens.
The aspheric spectacle lens is such that the pupil can line up with a portion of reading power that is most appropriate for that certain reading distance, thereby eliminating all of the distance rays and many unwanted other rays of light. The simultaneous, aspheric, multifocal contact lens must accept all rays, distance and near, because they are entering the pupil at one and the same time. Without a spherical, well-focused reading portion that can be measured in the lensometer, reading is compromised.
The point where the reading power starts on the lens is imperceptible to gross inspection. These aspheric (progressive) lenses offer excellent distance vision and good reading characteristics occur when the pupil is in line with the part of the lens that is most optically correct for the distance of the reading task. The reading vision power, however, is not as good as if one were looking through a spherical lens focused for that exact distance.
It has also been known to provide aspheric, simultaneous, multifocal contact lenses with the far vision in the center of the lens and progressively more reading power from the center to the edge. The lensometer can record the distance power, but fails on the reading power.
It is also known that the lensometer is somewhat analogous to the eye. A lens power that focuses poorly, or not at all, in the lensometer will not provide optimum vision for the person using the same.
It has been known that the shape of the human cornea is generally spherical.
It has been known that an aspheric curve is generally cone-shaped and when applied to fitting the cornea, exhibits a xe2x80x9cdunce capxe2x80x9d type fit that bears heavily on an annular zone generally adjacent to the mid-periphery of the cornea. This can result in corneal molding that is physiologically unhealthy and optically undesirable if the wearer wants to use his or her back-up spectacles at any time.
It has also been known to have bifocal contact lenses. See generally, U.S. Pat. Nos. 4,704,016; 4,890,913; 5,151,723; and 5,798,817. U.S. Pat. No. 4,890,913 discloses a multifocal contact lens having a plurality of concentric viewing zones, some of which are adapted for near vision and others for distant vision. It is stated to be an objective to provide the zones such that substantially equal amounts of light enter the eye through both the near and distant zones. One of the objectives was said to be in constructing the concentric zones to form alternating steeper and flatter curves such that a continuous tear film exists between the cornea and the back of the lens. The disclosure suggests manufacture of the lens by machining on a lathe or by molding. A number of resinous materials are identified. See also, U.S. Pat. No. 4,704,016 with respect to which U.S. Pat. No. 4,890,913 was a continuation-in-part application. U.S. Pat. No. 4,704,016 also discloses different types of distinct zones for near and distant vision.
U.S. Pat. No. 5,798,817 discloses bifocal contact lenses having a plurality of near vision zones and a plurality of distant vision zones. At least one of the near vision zones was said to be an aspherical, lenticular surface.
U.S. Pat. No. 5,151,723 discloses a multifocal contact lens. It states that there have been known previously three principal types of bifocal contact lenses. One is simultaneous vision or concentric lenses. The second is alternating vision lenses, and the third is diffraction or halographic lenses. It also states that is has been known to provide simultaneous vision lenses which are physically symmetric in design and are manufactured with a central zone having prescriptive power suitable for a patient""s distant vision and a peripheral rim of a different prescriptive value for a patient""s near vision.
Despite the foregoing, there remains a very real and substantial need for an improved multifocal contact lens which permits simultaneous distance and near vision and provides additional benefits, such as elimination of a pronounced line of demarcation between adjacent zones.
The present invention has met the above-described need by providing a multifocal contact lens having a transparent lens body provided with an inner concave surface and an outer convex surface. In the preferred embodiment an aspheric central portion is structured to provide distance vision, and an adjacent annular spherical portion is structured to provide near vision. The aspheric central portion of the lens has a progressively flattened curve as it extends toward the radially inner part of the spherical portion and has a radius substantially equal to the adjacent radially inner portion of the spherical portion and thereby eliminates the objectionable visible junction therebetween.
In a preferred embodiment, the aspherical central portion will be formed within the inner surface of the lens, as will the annular spherical portion.
In an alternate embodiment, the central aspherical portion and spherical portion may be formed in the outer surface of the lens.
In another embodiment a spherical reading central portion and an outer aspherical distance portion may be employed without a pronounced line therebetween.
The invention also provides a method of manufacturing a multifocal contact lens which includes creating a contact lens blank having an outer surface and an inner surface creating a generally spherical concave configuration in the inner surface, converting the center portion of the generally spherical concave inner surface into an aspherical configuration, converting a portion of said inner surface disposed radially outwardly of said center portion into a spherical concave portion, and creating a generally spherical convex configuration in said outer surface.
The method may also include establishing a central spherical reading portion and an outer said aspherical distance portion adjacent to the central generally spherical adjacent portion.
It is an object of the present invention to improve multifocal contact lenses for simultaneous distant and near vision.
It is a further object of the present invention to provide such a contact lens which has an aspherical inner portion structured for distance vision to intermediate near vision with an adjacent annular spherical portion structured for near reading.
It is another object of the present invention to provide such a multifocal lens which has only one single distance to intermediate vision portion and only one single near-reading vision portion.
It is a further object of the present invention to provide a method of making such a lens.
It is a further object of the present invention to provide such a lens which may be made of conventional materials using previously known techniques adapted to the method of the present invention.
It is yet another object of the present invention to provide a multifocal contact lens with in-focus, non-clashing, rays of light which originate from distance to reading distances and all points in between.
It is a further object of the present invention to provide such a contact lens which does not have an objectionable, visually perceptible line of demarcation between the distant vision and near vision portions.
These and other objects of the present invention will be more fully understood from the description of the invention with reference to the drawings appended hereto.